Archive for September, 2009

One of the most frequently visited pages on Conscious Entities is this account of Benjamin Libet’s remarkable experiments, which seemed to show that decisions to move were really made half a second before we were aware of having decided. To some this seemed like a practical disproof of the freedom of the will – if the decision was already made before we were consciously aware of it, how could our conscious thoughts have determined what the decision was? Libet’s findings have remained controversial ever since they were published; they have been attacked from several different angles, but his results were confirmed and repeated by other researchers and seemed solid.

However, Libet’s conclusions rested on the use of Readiness Potentials (RPs). Earlier research had shown that the occurence of an RP in the brain reliably indicated that a movement was coming along just afterwards, and they were therefore seen as a neurological sign that the decision to move had been taken (Libet himself found that the movement could sometimes be suppressed after the RP had appeared, but this possibility, which he referred to as ‘free won’t ‘, seemed only to provide an interesting footnote). The new research, by Trevena and Miller at Otago, undermines the idea that RPs indicate a decision.

Two separate sets of similar experiments were carried out. They resembled Libet’s original ones in most respects, although computer screens and keyboards replaced Libet’s more primitive equipment, and the hand movement took the form of a key-press. A clock face similar to that in Libet’s experiments was shown, and they even provided a circling dot. In the earlier experiments this had provided an ingenious way of timing the subject’s awareness that a decision had been made – the subject would report the position of the dot at the moment of decision – but in Trevena and Miller’s research the clock and dot were provided only to make conditions resemble Libet’s as much as possible. Subjects were told to ignore them (which you might think rendered their inclusion pointless). This was because instead of allowing the subject to choose their own time for action, as in Libet’s original experiments, the subjects in the new research were prompted by a randomly-timed tone. This is obviously a significant change from the original experiment; the reason for doing it this way was that Trevena and Miller wanted to be able to measure occasions when the subject decided not to move as well as those when there was movement. Some of the subjects were told to strike a key whenever the tone sounded, while the rest were asked to do so only about half the time (it was left up to them to select which tones to respond to, though if they seemed to be falling well below a 50-50 split they got a reminder in the latter part of the experiment). Another significant difference from Libet’s tests is that left and right hands were used: in one set of experiments the subjects were told by a letter in the centre of the screen whether they should use the right or left hand on each occasion, in the other it was left up to them.

There were two interesting results. One was that the same kind of RP appeared whether the subject pressed a key or not. Trevena and Miller say this shows that the RP was not, after all, an indication of a decision to move, and was presumably instead associated with some more general kind of sustained attention or preparing for a decision. Second, they found that a different kind of RP, the Lateralised Readiness Potential or LRP, which provides an indication of readiness to move a particular hand, did provide an indication of a decision, appearing only where a movement followed; but the LRP did not appear until just after the tone. This suggests, in contradiction to Libet, that the early stages of action followed the conscious experience of deciding, rather than preceding it.

The differences between these new experiments and Libet’s originals provide a weak spot which Libetians will certainly attack. Marcel Brass, whose own work with fMRI scanning confirmed and even extended Libet’s delay, seeming to show that decisions could be predicted anything up to ten seconds before conscious awareness, has apparently already said that in his view the changes undermine the conclusions Trevena and Miller would like to draw. Given the complex arguments over the exact significance of timings in Libet’s results, I’m sure the new results will prove contentious. However, it does seem as if a significant blow has been struck for the first time against the foundations of Libet’s remarkable results.

The first part of the paper provides a nice, gentle introduction to the issue of qualia in dialogue form. Elitzur explains the bind that we’re in in this respect: we seem to have an undeniable first-hand experience of qualia, yet they don’t fit into the normal physical account of the world. We seem to be faced with a dilemma: either reject qualia – perhaps we just misperceive our percepts as qualia – or accept some violation of normal physics. The position is baffling: but Elitzur wants to suggest that that very bafflement provides a clue. His strategy is to try to drag the issue into the realm of science, and the argument goes like this:

1. By physicalism, consciousness and brain processes are identical.
2. Whence, then, the dualistic bafflement about their apparent nonidentity?
3. By physicalism, this nonidentity, and hence the resultant bafflement, must be due to error.
4. But then, again by physicalism, an error must have a causal explanation.
5. Logic, cognitive science and AI are advanced enough nowadays to provide such an explanation for the alleged error underlying dualism, and future neurophysiology must be able to point out its neural correlate.

That last point seems optimistic. Cognitive science may be advanced enough to provide explanations for a number of cognitive deficits and illusions, but sometimes only partial ones; and not all errors are the result of a structural problem. It’s particularly optimistic to think that all errors must have an identifiable neural correlate. But this seems to be what Elitzur believes. He actually says

“When future neurophysiology becomes advanced enough to point out the neural correlates of false beliefs, a specific correlate of this kind would be found to underlie the bafflement about qualia.”

The neural correlates of false beliefs? Crikey! It’s perfectly reasonable to assume that all false beliefs have neural correlates – because one assumes that all beliefs do – but the idea that false ones can be distinguished by their neural properties is surely evidently wrong. An argument hardly seems required, but it’s easy, for example, to picture a man who believes a coin has come down heads. If it has, his belief is true, but if it’s actually tails, exactly the same belief, with identical neural patterns would be false. I think Elitzur must mean something less startling than what he seems to be saying; he must, I think, take it as read that if qualia are a delusion, they would be a product of some twist or quirk in our mental set-up. That’s not an unreasonable position, one that would be shared by Metzinger, for example (discussion coming soon).

As it happens, Elitzur doesn’t think qualia are delusions; instead he has an argument which he thinks shows that interactionist dualism – a position he doesn’t otherwise find very attractive – must be true. The argument is to do with zombies. Zombies in this context, as regular readers will know, are people who have all the qualities normal people posess, except qualia. Because qualia have no physical causal effects, the behaviour of zombies, caused by normal physical factors, is exactly like that of normal people. Elitzur quotes Chalmers explaining that zombie-Chalmers even talks about qualia and writes philosophical papers about them, though in fact he has none. The core of Elitzur’s position is his incredulity over this conclusion. How could zombies who don’t have qualia come to be worried about them?

It is an uncomfortable position, but if we accept that zombies are possible and qualia exist, Chalmers’ logic seems irrefutable. Ex hypothesi, zombies follow the same physical laws as us: it’s ultimately physics that causes the movements of our hands and mouths involved in writing or speaking about qualia: so our zombie counterparts must go through the same motions, writing the same books and emitting the same sounds. Since this seems totally illogical to Elitzur, he offers the rationalisation that when zombies talk about qualia, they must in fact merely be talking about their percepts. But this asymmetry provides a chink which can be used to prose zombies and qualiate people apart. If we ask Chalmers whether his zombie equivalent is possible, he replies that it is; but, suggests Elitzur, if we ask zombie Chalmers (whom he call ‘Charmless’) the same question, he replies in the negative. Chalmers can imagine himself functioning without qualia, because qualia have no functional role: but Charmless cannot imagine himself functioning without percepts, because percepts are part of the essence of his sensory system. (It is possible to take the analogous view about qualia of course – namely that zombies are impossible, because a physically identical person just would necessarily have the same qualia). So zombies differ from us, oddly enough, in not being able to conceive of their own zombies.

For Elitzur, the conclusion is inescapable; qualia do have an effect on our brains. He chooses therefore to bite the bullet of accepting that the laws of physics must be messed up in some way – that where qualia intervene, conservation laws are breached, unpalatable as this conclusion is. One consoling feature is that if qualia do have physical effects, they can be included in the evolutionary story; perhaps they serve to hasten or intensify our responses: but overall it’s regrettable that dualism turns out to be the answer.

I don’t think this is a convincing conclusion; it seems as if Elitzur’s incredulity has led him into not taking the premises of the zombie question seriously enough. It just is the case ex hypothesi that all of our zombies’ behaviour is caused by the same physical factors as our own behaviour; it follows that if their talk about qualia is not caused by qualia, neither is ours (note that this doesn’t have to mean that either we or the zombies fail to talk about qualia). There are other ways out of this uncomfortable position, discussed by Chalmers (perhaps, for example, our words about qualia are over-determined, caused both by physical factors and by our actual experiences). My own preferred view is that whatever qualia might be, they certainly go along with certain physical brain functions, and that therefore any physical duplicate of ourselves would have the same qualia; that zombies, in other words, are not possible. It’s just a coincidence, I’m sure, that in Elitzur’s theory this is the kind of thing a zombie would say…